A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
A type of actuator that is well-known in the state of the art is a ‘reluctance actuator’. A magnetic flux may for example be generated by applying an electrical current through a coil, wherein the path of the magnetic flux forms a loop depending on the reluctance of the surrounding materials. The magnetic flux is concentrated around the path of least reluctance. The concentration of magnetic flux in low-reluctance materials forms strong temporary poles and causes mechanical forces that tend to move the materials towards regions of higher magnetic flux causing an attractive force. It is also known that reluctance actuators have a very high power density at low-cost, making them ideal for many applications. High power density actuators may for example be used in a lithographic apparatus, while accelerating and decelerating a mask stage, as proposed in U.S. Pat. No. 7,352,149. The use of reluctance actuators has however been limited by the complexity inherent in both design and controllability, which results in a high power density actuator concept but with less accuracy in comparison with e.g. well-known voice coil actuators.